In recent years, a number of bioorthogonal reactions have been developed, exemplified by click chemistry, that enable the efficient formation of a specific product, even within a highly complex ...chemical environment. While the exquisite selectivity and reliability of these transformations have led to their broad application in diverse research areas, they have proven to be particularly beneficial to biological studies. In this regard, the ability to rationally incorporate reactive tags onto a biomolecular target and subsequently achieve high selectivity in tag derivatization within a complex biological sample has revolutionized the toolbox that is available for addressing fundamental issues. Herein, an introduction to the impact of click chemistry and other bioorthogonal reactions on the study of biological systems is presented. This includes discussion of the philosophy behind click chemistry, the details and benefits of bioorthogonal reactions that have been developed, and examples of recent innovative approaches that have effectively exploited these transformations to study cellular processes. For the latter, the impacts of bioorthogonal reactions on drug design (i.e., in situ combinatorial drug design), biomolecule labeling and detection (site-specific derivatization of proteins, viruses, sugars, DNA, RNA, and lipids), and the recent strategy of activity-based protein profiling are highlighted.
Liposomes are effective nanocarriers due to their ability to deliver encapsulated drugs to diseased cells. Nevertheless, liposome delivery would be improved by enhancing the ability to control the ...release of contents at the target site. While various stimuli have been explored for triggering liposome release, enzymes provide excellent targets due to their common overexpression in diseased cells. We present a general approach to enzyme‐responsive liposomes exploiting targets that are commonly aberrant in disease, including esterases, phosphatases, and β‐galactosidases. Responsive lipids correlating with each enzyme family were designed and synthesized bearing an enzyme substrate moiety attached via a self‐immolating linker to a non‐bilayer lipid scaffold, such that enzymatic hydrolysis triggers lipid decomposition to disrupt membrane integrity and release contents. Liposome dye leakage assays demonstrated that each enzyme‐responsive liposome yielded significant content release upon enzymatic treatment compared to minimal release in controls. Results also showed that fine‐tuning liposome composition was critical for controlling release. DLS analysis showed particle size increases in the cases of esterase‐ and β‐galactosidase‐responsive lipids, supporting alterations to membrane properties. These results showcase an effective modular strategy that can be tailored to target different enzymes, providing a promising new avenue for advancing liposomal drug delivery.
A modular approach is reported for the development of enzyme‐responsive liposomes. These exploit synthetic lipid switches containing variable enzyme substrates that, when removed, yield decomposition of a self‐immolating linker producing a non‐bilayer lipid that perturbs the membrane and triggers release of contents. This approach enables the targeting of a range of enzymes that are overexpressed in diseased cells for drug‐delivery applications (see figure).
Conspectus The ability to exert control over lipid properties, including structure, charge, function, and self-assembly characteristics is a powerful tool that can be implemented to achieve a wide ...range of biomedical applications. Examples in this arena include the development of caged lipids for controlled activation of signaling properties, metabolic labeling strategies for tracking lipid biosynthesis, lipid activity probes for identifying cognate binding partners, approaches for in situ membrane assembly, and liposome triggered release strategies. In this Account, we describe recent advancements in the latter area entailing the development of stimuli-responsive liposomes through programmable changes to lipid self-assembly properties, which can be harnessed to drive the release of encapsulated contents toward applications including drug delivery. We will focus on an emerging paradigm involving liposomal platforms that are sensitized toward chemical agents ranging from metal cations to small organic molecules that exhibit dysregulation in disease states. This has been achieved by developing synthetic lipid switches that are designed to undergo programmed conformational changes upon the recognition of specific target analytes. These structural alterations are leveraged to perturb the packing of lipids within the membrane and thereby drive the release of encapsulated contents. We provide an overview of the inspiration, design, and characterization of liposomes that selectively respond to wide-ranging target analytes. This series of studies began with the development of calcium-responsive liposomes utilizing a lipid switch inspired by sensors including indo-1. Following this successful demonstration, we next showed that the selectivity of the lipid switch could be altered among different metal cations by producing a liposomal platform for which release is induced through zinc binding. Our next goal was to develop metabolite-responsive liposomes in which switching is driven by molecular recognition events involving phosphorylated small molecules. In this work, screening of lipid switches designed to interact with phosphorylated metabolites led to the identification of liposomal formulations that selectivity release contents in the presence of adenosine triphosphate (ATP). Finally, we were able to modulate the metabolite selectivity by rationally designing a modified lipid switch structure that is activated through complexation of inositol-(1,4,5)-trisphosphate (IP3). These projects show the progression of our approaches for liposome release triggered by molecular recognition principles, building from ion-responsive lipid switches to structures that are activated by small molecules. These “smart” liposomal platforms provide an important addition to the toolbox for controlled cargo release since they respond to ions or small molecules that are commonly overproduced by diseased cells.
Liposomes have proven to be effective nanocarriers due to their ability to encapsulate and deliver a wide variety of therapeutic cargo. A key goal of liposome research is to enhance control over ...content release at diseased sites. Though a number of stimuli have been explored for triggering liposomal release, reactive oxygen species (ROS), which have received significantly less attention, provide excellent targets due to their key roles in biology and overabundance in diseased cells. Here, we report a ROS-responsive liposome platform through the inclusion of lipid 1 bearing a boronate ester headgroup and a quinone-methide (QM) generating self-immolative linker attached onto a dioleoylphosphatidylethanolamine (DOPE) lipid scaffold. Fluorescence-based dye release assays validated that this system enables release of both hydrophobic and hydrophilic contents upon hydrogen peroxide (H2O2) addition. Details of the release process were carefully studied, and data showed that oxidative removal of the boronate headgroup is sufficient to result in hydrophobic content release, while production of DOPE is needed for hydrophilic cargo leakage. These results showcase that lipid 1 can serve as a promising ROS-responsive liposomal delivery platform for controlled release.
Display omitted
In this work, we report the design, synthesis, and application of a bis-pyrene phospholipid probe for detection of phospholipase A2 action through changes in pyrene monomer and ...excimer fluorescence intensities. Continuous fluorometric assays enabled detection of the activities of multiple PLA2 enzymes as well as the decrease in catalysis by PLA2 from honey bee venom caused by the inhibitor p-bromo phenacylbromide. Thin-layer chromatography and mass spectrometry analysis were also used to validate probe hydrolysis by PLA2. Mass spectrometry data also supported cleavage of the probe by phospholipase C and D enzymes, although changes in fluorescence were not observed in these cases. Nevertheless, the bis-pyrene phospholipid probe developed in this work is effective for detection of PLA2 enzyme activity through an assay that enables screening for inhibitor development.
Advancements in the field of liposomal drug carriers have culminated in greatly improved delivery properties. An important aspect of this work entails development of designer liposomes for release of ...contents triggered by environmental changes. The majority of these systems are driven by chemical reactions in the presence of different stimuli. However, a promising new paradigm instead focuses on molecular recognition events as the impetus for content release. In certain cases, these platforms exploit synthetic lipid switches designed to undergo conformational changes upon binding to target ions or molecules that perturb membrane assembly, thereby triggering cargo release. Examples of this approach reported thus far showcase how rational design of lipid switches can result in dramatic changes in lipid assembly properties. These strategies show great promise for opening up new pathophysiological stimuli that can be harnessed for programmed content release in drug delivery applications.
Cell‐type‐specific drug delivery: This concept article describes recent advancements in the development of stimuli‐responsive liposomes specifically driven by synthetic lipid analogs that undergo conformational changes upon binding interactions that trigger the release of entrapped cargo from liposomes. This enables the development of liposomes that release contents in the presence of increased concentrations of specific atomic or molecular species as a novel means for enhancing cell‐type‐specific drug delivery.
•Stimuli-responsive liposomes have been developed by engineering lipids that change properties under disease conditions.•One strategy of lipid switch design hinges upon the production of non-bilayer ...lipids in the presence of stimuli.•Artificial lipids have also been reported that undergo significant conformational changes upon stimulus treatment.•A variety of stimulus conditions have been explored for driving release of encapsulated cargo from liposomes.•Stimuli-responsive liposomes show strong prospects for enhancing selectivity for drug delivery to diseased cells.
While liposomes have proven to be effective drug delivery nanocarriers, their therapeutic attributes could be improved through the development of clinically viable triggered release strategies in which encapsulated drug contents could be selectively released at the sites of diseased cells. As such, a significant amount of research has been reported involving the development of stimuli-responsive liposomes and a broad range of strategies have been explored for driving content release. These have included the introduction of trigger groups at either the lipid headgroup or within the acyl chains that alter lipid self-assembly properties of known lipids as well as the rational design of lipid analogs programed to undergo conformational changes induced by events such as binding interactions. This review article describes advances in the design of stimuli-responsive liposome strategies with an eye towards emerging trends in the field.
•Modeled variation of building mix and energy supply technology endogenously.•Optimized district-scale energy supply and demand simultaneously.•Case study with CHP engines, chillers, and 21 building ...types run for San Francisco.•Potential to achieve over 70% efficiency with low carbon emissions and low cost.•Ability to provide decision support for urban planners and infrastructure designers.
Reducing the energy consumption and associated greenhouse gas emissions of urban areas is paramount in research and practice, encompassing strategies to both reduce energy consumption and carbon intensity in both energy supply and demand. Most methods focus on one of these two approaches but few integrate decisions for supply and demand simultaneously. This paper presents a novel model that endogenously simulates energy supply and demand at a district scale on an hourly time scale. Demand is specified for a variety of building uses, and losses and municipal loads are calculated from the number of buildings in the district. Energy supply is modeled using technology-specific classes, allowing easy addition of specific equipment or types of energy generation. Standard interfaces allow expansion of the model to include new types of energy supply and demand. The model can be used for analysis of a single design alternative or optimization over a large design space, allowing exploration of various densities, mixes of uses, and energy supply technologies. An example optimization is provided for a community near San Francisco, California. This example uses 21 building types, 32 combined heat and power engines, and 16 chillers. The results demonstrate the ability to compare performance trade-offs and optimize for three objectives: life cycle cost, annual carbon dioxide emissions, and overall system efficiency.
Liposomes are effective nanocarriers due to their ability to encapsulate and deliver a wide variety of therapeutics. However, therapeutic potential would be improved by enhanced control over the ...release of drug cargo. Zinc ions provide exciting new targets for stimuli-responsive lipid design due to their overly abundant concentrations associated with diseased cells. Herein, we report zinc-triggered release of liposomal contents exploiting synthetic lipid switches designed to undergo conformational changes in the presence of this ion. Initially, Nile red leakage assays were conducted that validated successful dose-dependent triggering of release using zinc-responsive lipids (ZRLs). In addition, dynamic light scattering and confocal microscopy experiments showed that zinc treatment led to morphological changes in lipid nanoparticles only when ZRLs were present in formulations. Next, zinc-binding experiments conducted in a solution (NMR, MS) or membrane (zeta potential) context confirmed ZRL-Zn complexation. Finally, polar cargo release from liposomes was achieved. The results from these wide-ranging experiments using four different compounds indicated that zinc-responsive properties varied based on ZRL structure, providing insights into the structural requirements for activity. This work has established zinc-responsive liposomal platforms toward the development of clinical triggered release formulations.
A stimuli-responsive liposomal platform that is selectively activated by inositol 1,4,5-trisphosphate (IP
3
) over eleven other phosphorylated metabolites is reported. Dye release assays validated ...dose-dependent release of both hydrophilic and hydrophobic cargo driven by IP
3
, showcasing the potential of this platform for triggered release and sensing applications.
Liposome cargo release triggered by IP
3
is achieved using a synthetic lipid switch designed to undergo conformational changes upon binding.
PDF
